Modern gas turbine engine augmentors operating at high exhaust gas inlet temperatures require that any hardware placed in the engine exhaust gas stream, specifically the augmentor fuel injectors and flameholders, be cooled to maintain the temperature of the hardware at a level compatible with the materials used. This requirement has resulted in prior art augmentor designs wherein individual fuel injector spraybars and flameholders are mounted about the circumference of the augmentor case and extend radially inward therefrom into the hot engine exhaust gas stream. Such an arrangement allows the individual structures to be cooled by the relatively low temperature fan air which typically flows in an annulus located adjacent the augmentor case and separated from the coaxial engine exhaust gas stream by an inner screech liner or similar barrier.
Such radial designs, while effective in cooling the spraybar or flameholder structures themselves, results in the establishment of active combustion immediately adjacent the inner surface of the augmentor liner downstream of the individual radial flameholders. The result of such combustion is a localized area of overtemperature in the liner, often termed a "hot spot" or "hot streak" which in turn causes localized conditions of thermal stress, premature wear, and a generally undesirable reduction in the liner service lifetime.
Prior art liner cooling solutions, such as distributing cooling holes over the liner to provide a transpiration cooling film by drawing the relatively cool fan air into the engine exhaust gas stream adjacent the inner liner, have not been adequately effective in the high heat release flame zone immediately downstream of the flameholder structure. The local liner overtemperature problem is identical whether the fuel injector and flameholder structures are distinct or combined.
What is needed is an effective means for locally protecting the augmentor liner immediately downstream of a radial flameholding structure.